This invention relates to systems for preventing damage to cargo shipped in air-ride suspension semi-trailer trucks loaded on railroad flat cars, commonly referred to as the "piggyback" method of railroad transportation, and more particularly to means for and methods of controlling the air-suspension system of the semi-trailers while in piggyback transportation.
Cargoes of a fragile nature are often transported by the household moving industry in semi-trailer trucks equipped with air-ride suspension rather than in trucks provided with conventional spring-type suspension systems. For example, furniture and household goods, computers, data processing equipment, telephone equipment, copying and duplicating equipment, electronic equipment, and the like are usually transported by air-ride suspension semi-trailer trucks because air-ride trucks provide a much smoother ride than conventional trucks, offering more protection against possible damage during transport.
Semi-trailer trucks equipped with air-ride suspension are often provided with four large air bags located between the underside of the semi-trailer body and the rear axles, one bag being located above each of the four sets of rear wheels. An air line from each bag extends to a central valve connected to the main air line. The main air line extends to the front of the semi-trailer where it is connected to a compressor mounted on the tractor used to pull the semi-trailer. The compressor is usually designed to maintain about 30 psi of pressure in each bag. When inflated, the air bags suspend the semi-trailer body above the rear axles and cushion the semi-trailer body and its contents against the vertical movement of the axles. The inflated air bags comprise the sole suspension system for the semi-trailer; no other suspension system is provided in air-ride trucks.
The central air valve is designed to maintain a constant level of pressure in each bag. This valve (part Nos. 90054114 and 90054113) is manufactured by Nu-Way Suspension Systems, Inc. of Muskegan, Mich. and can be purchased commercially." For example, when a set of wheels passes over a bump in the road the air bag situated above the wheels is compressed. To maintain equilibrium in the ride of the semi-trailer, air exhausts from the compressed bag through the central valve. When the wheels move downwardly after passing over the bump, air is supplied to the bag as it returns to its normal volume. In addition, when a rough road causes the wheels on one side of the semi-trailer to move upwardly and those on the other side to move downwardly, the central air valve supplies air to the air bags in a manner which enables the semi-trailer to maintain its equilibrium and avoid lateral sway. The central valve enables air to pass from the air bags which are being compressed by the upwardly moving wheels to the air bags which have room to expand above the downwardly moving wheels, thereby maintaining a level semi-trailer bed. When the wheels return to their normal position, the air valve enables the air to return from the formerly expanded air bags to the formerly compressed air bags. Thus, the semi-trailer is prevented from swaying from side to side.
Due to a certain amount of leakage inherent in the system and the exhausting of air that occurs as the wheels travel over bumps in the road, a constant supply of air must be provided to maintain the pressure in the air bags.
Transportation of goods by the piggyback method is efficient and economical. It combines many of the best features of railroad and highway transportation. For example, transportation of cargo by truck enables delivery and pick up at locations which cannot be reached by a rail line or spur; however, trucks cannot carry cargo over long distances as economically as rail transportation. Railroads use approximately 600 to 800 BTU's per ton mile to transport cargo by flat car while a diesel truck uses approximately 2000 to 2100 BTU's per ton mile to transport the same cargo. Hence, the amount of energy required to ship cargo by rail often averages about 50% to 60% less than the energy required when transportation is exclusively by truck. There is also a savings in manpower since a separate driver is not required for each truck while it is being carried by a train. In addition, the piggyback method provides a quick and efficient means for loading cargo on a train.
Despite the many advantages of the piggyback method of transporting cargo, a serious problem exists making it impractical to transport by the piggyback method the fragile types of cargo usually carried in air-ride suspension semi-trailer trucks. Presently, air-ride suspension semi-trailers are not mounted on railroad flat cars for transportation by the piggyback method since there is no readily obtainable source of compressed air to inflate the air bags. Although compressed air is used in the train's braking system, use of this supply of air can create problems.Bleeding off air from the braking system must be carefully controlled to prevent unwanted activation of the train's air brakes.
Because the air bags located under the air-ride semi-trailer would not be inflated when the semi-trailer is mounted on the railroad car, the lateral sway and rough ride frequently encountered during rail transport would cause severe damage to the cargo contained in the semi-trailer. Furthermore, it is not practical to transport the fragile type of cargo usually carried in air-ride trucks by the piggyback method in trucks equipped with conventional suspension systems. Conventional truck suspension systems are not adequate to protect such fragile cargo from damage caused by the lateral sway and rough ride encountered in rail transport. Thus, there is a need for a system to inflate the air bags of an air-ride suspension semi-trailer during transport by the piggyback method to prevent damage to the goods carried in the semi-trailer.
Accordingly, an object of the present invention is to provide new and improved systems for protecting cargo from being damaged during transport by the piggyback method by utilizing the air-ride suspension systems of semi-trailers while they are mounted on railroad flat cars.
A further object of our invention is to provide systems for operating the air-ride suspension systems of semi-trailers while they are mounted on railroad flat cars by utilizing the compressed air in the brake line of a freight train.
Another object of our invention is to provide systems for operating the air-ride suspension systems of semi-trailers while they are mounted on railroad flat cars by utilizing the compressed air in the brake line of freight trains, while preventing the brakes of the trains from being activated when the compressed air is bled off.
In the preferred embodiment of our invention, an air-ride semi-trailer truck is mounted on a railroad flat car provided with an air reservoir. The air reservoir is connected to the train brake line by means of a coupling element which enables air to be bled off from the brake line without activating the train brakes. The coupling element is provided with a valve which prevents compressed air from the train brake line from flowing to the air reservoir when the air pressure in the brake line falls below a predetermined safety level. The valve also prevents air from flowing from the air reservoir to the brake line.
The air reservoir is also connected to the air-ride suspension system of the semi-trailer and provides compressed air, obtained from the train brake line, to inflate the air bags and thus suspend the semi-trailer body above the rear axles. The semi-trailer body is thus cushioned by the air bags against the rough ride and lateral sway of the train. A regulator valve disposed in the air line connecting the air reservoir to the air-ride suspension system measures the air pressure in the air bags and insures that a constant fixed pressure is maintained in the air bags by the air reservoir.